Various types of surgical procedures are currently performed to investigate, diagnose, and treat diseases involving a tissue or organs located in a patient's thoracic cavity (e.g., the heart, lungs, and the like). Using current techniques, many of those procedures typically require a partial or median sternotomy to gain access into the patient's thoracic cavity. A partial or median sternotomy is a procedure by which a saw or other appropriate cutting instrument is used to make a midline, longitudinal incision along a portion or the entire axial length of the patient's sternum, allowing two opposing sternal halves to be separated laterally. A large opening into the thoracic cavity is thus created, through which a surgeon may directly visualize and operate upon the heart and other thoracic organs or tissues.
Following the surgical procedure within the thoracic cavity, the two severed sternal halves must be reapproximated (closed). Traditionally, the sternal halves have been reapproximated with stainless steel wires which are wrapped around or through the sternal halves so as to exert medial compression thereon and twisted together to approximate the sternum. Other methods of sternum repair include the use of band or strap assemblies. Such assemblies typically include a locking mechanism, which secures a strap in a closed looped configuration about the sternum positions. While utilization of steel wires and strap assemblies have been widely accepted for sternum repair, these devices present a number of disadvantages. Steel wires can and do break, and provide insufficient (non-uniform) clamping force resulting in sternal nonunion. Steel wires are difficult to maneuver and place around the sternum. The cut ends of the steel wires are also sharp and can pierce through the surgeon's gloves or fingers. In addition, the small diameter of the steel wires can cause the wires to migrate into or through the tissue surrounding the sternum region or into the sternal bone itself over time. This can lead to significant patient pain and discomfort in addition to slowing the postoperative recovery and increasing the risk of sternal infection. Moreover, the strap mechanisms of band assemblies are often relatively structurally complex and are difficult to precisely apply about the sternum. There are also healing problems associated with the use of steel wires and band assemblies due to improper forces exerted by these devices which can cause unwanted bone movements leading to raking and rubbing of surrounding tissue or bone.
Several other techniques of sternal reapproximation have been proposed both for primary closure following a median sternotomy and for reclosure following post-operative emergency surgical procedures. One such sternal fixation device is described in Brown, R. P., Esmore, D. S., and Lawson, C., Improved Sternal Fixation in the Transternal Bilateral Thoracotomy Incision, J. Thoracic Cardiovascular Surg. 1996, Volume 112, number 1, the entire contents of which are incorporated herein by reference. The device described therein is composed of two plates, one anterior and one posterior to the sternum, that are fixed to each other and to the sternum by means of screws into internally threaded posts positioned in predrilled holes through the bone on either side of the sternotomy. This device, and others similar to it, are not optimal, however, because they require direct fixation of the plates to the bone with screws. This makes reentry into the thoracic cavity through the sternotomy extremely difficult if a medical emergency arises during the surgical procedure or post-operative requiring relatively quick access to the organs and/or tissues within the patient's thoracic cavity.
To overcome the problems inherent in direct fixation devices, another technique of sternal reapproximation has been proposed which employs overlapping sternal plates which can be removably joined to one another. In Hendrickson, S. C., Koger, K. E., Morea, C. J., Aponte, R. L., Smith, P. K., and Levin, S. L., Sternal Plating for the Treatment of Sternal Nonunion, Ann. Thor. Surg. 1996:62:512-8, the entire contents of which are incorporated by reference herein, a separable sternal clamping device is disclosed which includes a pair of opposed stainless steel sternal clamp plates which include respective generally J or C-shaped sternal engagement legs. The sternal clamp plates are laterally adjustable relative to one another but can be rigidly joined by, for example, a set of machine screws. The threaded coupling of the machine screws with the sternal plates removably secures the plates one to another in overlapping relationship without lateral shifting occurring over time, allowing easy reopening of the sternum if necessary.
Other improvements to sternal clamping devices and methods for sternal reapproximation are needed which are easily assembled, and which provide a stable and uniform clamping force and a well-approximated closure that allows bone healing to occur. The devices and methods should facilitate reopening of the sternum if necessary, e.g., in case of a medical emergency requiring the surgeon to have access to the patient's thoracic cavity. Preferably, the devices should be made from a biocompatible, radiolucent material which facilitates post-operative radioscopic viewing of the thoracic cavity. The lateral dimension between the clamp members of the devices should also be adjustable to fit a particular patient's sternum. New surgical tools are also required to assist the surgeon in properly tensioning the clamping device during the reapproximation procedure and for measuring the thickness of the sternal halves so that the surgeon can select the optimum sizes of the clamp member pairs for reapproximating the sternum.